1. Field of the Invention
The present invention relates to a method of producing a hose of natural or synthetic rubber, whereby the hose has an inner surface or core made of a foil or thin sheet of thermoplastic synthetic material that is resistant to solvent. The method includes the steps of disposing a foil tube or sleeve on a fabrication mandrel, then building-up on the foil sleeve a hose blank, with or without a reinforcement layer, and subsequently vulcanizing the hose blank, which simultaneously produces a bond between the hose blank and the foil sleeve.
2. Description of the Prior Art
It is known, and has also for a long time been the customary practice, to provide rubber hoses with inner linings made of synthetic material that is resistant to solvent to thereby make the hose usable for conveying chemically corrosive liquids such as acids or bases, mineral oil or petroleum products, refrigerants, dyes, etc. The requirement for the chemical resistance of the inner lining is to a large extent taken into account by the appropriate selection of the synthetic material, for example polyamide, polyethylene, or a halogen-substituted hydrocarbon, whereas on the other hand the necessary resistance to pressure, flexibility, and other characteristics of the hose are achieved with elements known in the hose-manufacturing industry. In all cases, the incorporation into the hose structure of a synthetic-material inner core, which is comparable to a foreign body, has always created problems. Since the inner core, which is generally manufactured in tubular form by extrusion or is formed by bending or winding foils or strips, for manufacturing reasons always must have a certain minimum thickness, this inner core imparts to the finished hose a relatively high rigidity. Although this problem can be remedied somewhat by embodying the hose as a corrugated hose that has corrugations that extend in the circumferential direction or helically, such a configuration is often not desirable from the standpoint of flow dynamics. In addition to the generally poor conditions for a satisfactory secure bonding of the paired rubber and synthetic material, the tendency exists to form folds and even localized tears during the course of the build-up of the hose, and especially during the subsequent vulcanization, representing conditions that have proven to be particularly difficult to deal with. This always latent danger of encountering these conditions could up to now be prevented only by a compromise in the selection of thicker inner cores, which consequently also resulted in stiffer inner cores.
An object of the present invention, via the introduction of a novel method feature, is to provide the prerequisites for the manufacture of high-grade rubber hoses that have an extremely thin-walled inner core that is made of chemically resistant synthetic material and that has a completely smooth inner surface that will not form folds.